1. Field of the Invention
The present invention relates to a method and an apparatus for the separation of mechanically connected parts made from different aluminum alloys, and more particularly to a method and an apparatus for separating the aluminum alloys that are commonly used to make aluminum alloy can ends from the aluminum alloys commonly used to make can bodies.
2. Description of the Related Art
In ever-increasing quantities, cans, including beverage cans, are being made from aluminum alloys because of the ease with which such materials can be formed into containers, and also because the lighter weight of these containers reduces shipping costs. One of the principal applications of aluminum alloy cans is for use as beverage containers. Typically, such beverage cans are of the usual cylindrical configuration having both top and bottom ends and a cylindrical body or sidewall.
The most prevalent process for forming such cans involves providing a disk-shaped blank of aluminum alloy that is deep drawn with a suitable pressing die to provide a can body open at one end and having a thin, cylindrical sidewall integrally connected with a thicker bottom end. The sidewall and bottom end are therefore made from the same material, which is generally Aluminum Association alloy number 3104 (AA3104).
The top ends of such aluminum alloy cans are separately formed from an aluminum alloy, typically Aluminum Association alloy number 5182 (AA5182), having a different chemical composition and different physical properties from that of AA3104. Further, the usual ring tabs and stay-on tabs for providing a dispensing opening to permit use of the contents of the can are typically also made from an Aluminum Association 5000-series alloy.
With the increasing emphasis upon preservation of the environment by the recycling of materials, there is strong support for recycling of plastic, glass, and metallic packaging materials, including used aluminum beverage cans (UBC's). However, because of the different aluminum alloys that are employed in making different parts of such cans, simply melting entire aluminum UBC's will provide a resulting material that lacks the desirable individual properties from which the parts of the original can were formed. Consequently, it is desirable that the can body alloys and the can end alloys be separated, to preserve as much as possible of the original alloy composition for use as scrap material to be added to virgin material for reuse. Otherwise, the melting of entire cans would require excessive subsequent modification of the resulting molten metal, such as, for example, the addition of primary aluminum metal to lower the percentage amounts of other alloying materials present, and the addition of other alloying elements necessary to provide a alloy having the desired composition and physical characteristics.
Various approaches have been suggested to permit the separation of different alloys from UBC's. For example, in U.S. Pat. No. 4,468,847, which issued on Sep. 4, 1984, to Kenneth A. Bowman et al., a method is disclosed for segregating metallic components of UBC's. The method includes first separating foreign materials, such as dirt, sand, coating materials, and the like. The resulting aluminum alloy UBC's are then heated to a temperature that is below the melting point of each of the alloys but that is sufficient to cause incipient melting of the lowest melting temperature component. While at that incipient melting temperature, the cans are agitated to cause fracture at the grain boundaries of the lower melting point alloy and thereby separate, by screening, the fragments of this lower melting point alloy from the remainder of the cans. However, the requirement to heat the cans requires large heating facilities, involves high energy costs, and results in excessive oxidation of the fragments.
Additional methods that also include heating of cans to the lowest incipient melting temperature component are disclosed in U.S. Pat. Nos. 4,491,473; 4,498,523; 4,592,511; in each of which Kenneth A. Bowman is designated either as sole or as a joint inventor.
Other methods proposed for the separation of aluminum alloys include that disclosed in U.S. Pat. No. 4,330,090, which teaches the separation of wrought and cast aluminum materials by heating a mixture of such materials to a temperature above the solidus temperature of the cast aluminum material, crushing the material to fragmentize the cast aluminum, and screening the crushed material to separate the cast aluminum from the wrought aluminum.
Additionally, U.S. Pat. No. 4,119,453 teaches a method for separating from waste material malleable metals, such as copper, aluminum, or the like, and also plastic materials, by grinding the materials to a predetermined size and then impacting the materials to form the malleable materials into spheroids that are subsequently separated by conventional separation devices.
It is an object of the present invention to provide an improved process for the separation from scrap aluminum beverage cans of the different aluminum alloys used to make parts of the cans.
It is a further object of the present invention to provide a method for separating fragments of aluminum alloy beverage cans that does not require the heating of the cans.
It is a still further object of the present invention to provide a method for the continuous separation of physically connected aluminum alloys at lower cost than previously-used methods.